Why do some areas experience lower voter turnout even under compulsory voting systems? This paper examines the impact of migration turnover – encompassing both in- and out-migration – on voter turnout across communities. While past research has focused on migrant/non-migrant differences or in-/out-migration separately, we propose that both migratory movements tend to decrease political participation due to increased transaction and social costs. Using surveys and a new panel dataset combining census and voting records from over 5,000 Brazilian municipalities, we identify a robust negative association between local migratory turnover and voter turnout. This relationship holds across various time frames, levels of aggregation, analytical approaches, and variable definitions. Individual-level data analyses further corroborate these results. Additional tests suggest social costs constitute a key mechanism deterring turnout. These findings highlight the need to consider the broader consequences of population mobility for democratic processes and representation, particularly in areas experiencing higher levels of turnover.